This application claims the priority of German Patent Application No. 29902514.4 filed Feb. 15, 1999, the disclosure of which is hereby fully incorporated by reference herein.
1. Field of the Invention
The present invention pertains to a device for transporting fluids, especially viscous adhesive or sealing materials, with a supply line which can be connected to a source of fluid, a cylinder which can be filled with fluid by means of the supply line, and a movable piston inside the cylinder for ejecting fluid which is in the cylinder into a discharge line which communicates with the interior of the cylinder. The piston has an axial fluid channel and can be moved by means of a piston rod which has an axial fluid channel, with an inlet valve positioned between the supply line and the cylinder which can optionally be moved to open and closed positions to release or interrupt the supply of fluid from the supply line to the interior of the cylinder.
2. Background of the Invention
Known devices generally related to the present invention are used in order to transport adhesives or other fluids in measured quantities. One such device is known from the disclosed German patent application DE 42 11 370 A1. In the known transport device, a piston which is connected to a hollow tappet, having an axial channel which is connected to the cavity of the tappet, can be moved by means of a pneumatic or hydraulic drive cylinder inside a transport cylinder in such a way that fluid from the transport cylinder is ejected through the fluid channel formed in the piston and the hollow tappet and into a flexible line. The disadvantages here are the relatively long flow paths of the fluid through the piston, the hollow tappet and the hose.
In addition, only a relatively imprecisely measured quantity of fluid can be transported by means of the pneumatic drive cylinder. An additional disadvantage consists in the fact that the known transport device is a relatively large construction due to the pneumatic cylinder which drives the displacement piston. Furthermore, the transport of the fluid is subject to variations, since the gas in the pneumatic cylinder is compressible and there can therefore be variations in pressure in the pneumatic cylinder and uneven movement of the piston.
From the public application papers for 20 38 369, a cylinder pump is known which has a piston which can be moved in a cylinder by means of a piston rod, where one end of the piston rod has threading which engages a rotatable threaded sleeve in order to axially move the piston rod and thus the piston. A disadvantage of this device is that so-called dead spaces can occur in the cylinder chamber, in which fluid collects and is not ejected from the cylinder chamber over the period of several strokes of the piston. Furthermore, because of the dead spaces there can be unwanted temperature changes in the fluid, due to the fact that a quantity of fluid which is the first to be drawn into the cylinder cools down within the cylinder, and is not pressed out of the cylinder chamber until the end of the ejection stroke of the piston, whereas fluid which is last drawn into the cylinder is the first to be pressed out of the cylinder chamber again with the help of the piston.
The present invention is based on the task of providing a device to transport the fluid which avoids the disadvantages of the state of technology and makes it possible to transport an exactly measured quantity of a fluid, having compact and simple construction, and which in particular makes it possible to transport small quantities of fluid.
The invention accomplishes this task by providing the fluid transport device with a threaded piston rod. The threading on the piston rod engages corresponding threading on a drive element which is mounted so that it can rotate and can be propelled in a rotating manner, so that the piston can be moved in a cylinder by means of rotating the drive element.
The advantages of the invention consist mainly in the fact that by means of the corresponding threading on the piston rod, which has an axial fluid channel, and the drive element, measured transport of fluid with very exactly adjustable transport flows is realized, and at the same time there is the guarantee that because of the fluid channels formed in both the piston and the piston rod it is possible to fill the interior of the cylinder through these interconnected fluid channels, so that a quantity of fluid which is the first to reach the interior of the cylinder, after flowing through the interior of the cylinder, is the first again to be ejected, without small or even larger quantities of fluid collecting in a dead space in the cylinder and remaining in the cylinder longer than other quantities of fluid (first-in-first-out principle). By means of the combination, in accordance with the invention, of a piston rod which can be propelled with the help of threads, and the piston rod which has a fluid channel and a piston which also has an axial fluid channel, a compact design is realized for the device.
In an especially preferred manner, the piston rod is designed as a hollow spindle with male threads, and the drive element is designed as a threaded sleeve with female threads, since in this manner the double function of the piston rod in the form of a hollow spindle which serves on the one hand as the supply line for feeding the fluid into the interior of the cylinder and on the other hand as a means of propulsion for moving or shifting the piston inside the cylinder in order to draw fluid into or press it out of the piston can be realized with an especially compact and simple design.
In a manner which is likewise preferred, the implementation variant just described is further advanced by having the threaded sleeve mounted in a fixed location by means of a roller bearing on a housing and propellable by means of an electric motor, and by having gears between the threaded sleeve and the electric motor. The threaded sleeve, which is engaged with the hollow spindle in order to move the threaded sleeve and the piston axially, is thereby permanently and precisely mounted, and because of the gearing it can be driven at relatively low rotational speed, depending on the desired quantity to be transported, so that the piston is shifted in the cylinder at relatively low speed, in order to be able to transport relatively small quantities. At the same time, because of the gears, which preferably provide for a reduction in the speed of the electric motor, when the rotary speed of the drive element is low a relatively high torque is guaranteed in the drive element, so that the piston is moved in the cylinder with a relatively high force, so that variations in transport quantity can largely be avoided even with highly viscous fluids.
A gear system of relatively simple and reliable design consists in a gearset with a toothed belt, which works together with a gear wheel which is coupled to the threaded sleeve and another gear wheel which is coupled to the drive shaft of the electric motor.
In an especially preferred manner there is provision for the fluid flow path between an end section of the hollow spindle at the opposite end from the piston and the supply line to be interruptible by means of the inlet valve, for the inlet valve to be movable together with the hollow spindle, and for the supply line to be in the form of a flexible hose. The inlet valve is moved to the open position in order to fill the interior of the cylinder, and in this position the piston is shifted in such a way that fluid flows into the interior of the cylinder through the hollow spindle and the fluid channel formed in the piston. After the piston has reached its end position, the inlet valve is closed, and in order to transport fluid the hollow spindle can now be moved together with the piston by rotating the drive element, with the effect that fluid is pressed from the interior of the cylinder into a discharge line, which is preferably connected directly to the cylinder. By means of the flexible hose, the movements of the hollow spindle and the inlet valve can be adjusted relative to a fixed fluid source without problem.
In accordance with an additional preferred variant form it is proposed that the hollow spindle be guided at its end opposite the piston, and if appropriate that the inlet valve be guided by means of a linear guide. By having the piston guided axially inside the cylinder, on the one hand, and having the hollow spindle guided by means of a linear guide on the other hand, the elements of the device which can be moved relative to a housing are guided reliably for the back-and-forth movement which is necessary for operation. At the same time, an anti-twist prevention is realized for the hollow spindle and the piston. In a purposeful and robust manner, the linear guide has two guide rods and several guide sleeves which slide on the guide rods.
In an additional alternative implementation form of the invention, the inlet valve can be activated pneumatically or magnetically, since for both of these variants only little design effort is necessary. In an especially preferred manner, the discharge line is connected directly to the interior of the cylinder, and connects downstream to the discharge line of a fluid applying device, so that a complete device for transporting and applying a fluid is realized which can be attached to a robot arm, so as to be able, for example, to apply adhesive to motor vehicle parts in the manufacture of automobiles.
Since heated adhesives and sealants may be processed in many industrial applications, in accordance with an additional refinement of the invention a heating system is provided to heat the cylinder, so that the adhesive or sealant is kept at a preset temperature, especially during intermittent operation with relatively long interruptions in transport.